systemd-resolved.service
systemd-resolved is a system service that manages network name resolution. It does so by generating /run/systemd/resolve/resolv.conf, which may be symlinked from /etc/resolv.conf. The contents is generated from the global settings in resolved.conf(5), the per-link static settings in .network files, and the per-link dynamic settings received over DHCP. See systemd.network(5) for more details.
Note that /run/systemd/resolve/resolv.conf should not be used directly, but only through a symlink from /etc/resolv.conf.
resolved.conf(5), systemd(1), systemd.network(5), systemd-networkd.service(8)